>Is it true that the compression ratio was increased on four >barrel engines. Does this even apply to the later models, as >late as the mid to late 70's? Is it done simply with pistons, >or did the heads change also?

I heard the reverse was true, I've never confirmed it. I happen to have quite a bit of experience here (bare with me). I first found this anomally in the pickups when I was overhauling my old mans '76 F350 factory flatbed. When I got it out it had a D4TE casting, "great ;-(" I figured it was a 391. I got it apart and found a standard crank snout and a 390 stamped crank. Here's where I got lost, when I pulled a piston out it was marked 410. Well, I did some checking with stuff laying around and found that the 410 piston did in fact have the same compression height as a 428 piston, I happened to have a 410 merc laying around so I verified paiston ID's and they were identical. I inquired with an old Ford parts man and some others and found that they listed 390-4V in pickups separately for this reason, I always wondered about that when I got spark plugs. It was literally an ultra low compression 390 at around 7.8:1. I thought that it was a little doggy even for 350K miles but this sure explained alot. After talking to my retired Ford parts buddy I found that they used 410 Merc pistons with the 390 crank to get the low compression ratio. So naturally I shelved the 390 crank, cleaned up a 428 crank, got Sealed Power 381P pistons (for $107 from Summit) and made myself a heavy duty 410 with all that wonderful compression. Since then I have found several pickup engines with this same low compression set up.

And From Shoe:
...at least some, if not all, late 360s got a special 360 piston which is exactly a 390-4V piston with NO DISH WHATSOEVER, just four 390-type valve reliefs.

If you want some cheap compression for your 390 (I'd guess 11.0:1 with pre-emissions heads), I wonder if buying a set of 1974ish 360+.030 cast pistons will get you an airplane-gas hungry 390 on-the-cheap.

Note that early 360s (1968-69 maybe) got full-skirt pistons, but Ford apparently realized they were wasting aluminum (and needing extra iron in the crankshafts to counterbalance it) with these pistons, so they seem to have abandoned the full-skirt somewhere around the turn of the 1970 decade, give or take a few years.

Shoe.


And from Bill Ballinger:

I think the 360s also use a thicker wrist pin. TRW makes, or at least used to, an L2291AF piston which duplicates the stock 390 4V and L2291F 390 piston(flat-top with eyebrows) with the only difference being a thicker pin.

 

That confirms what I heard about the lowered compression ratios. I am one that agrees with a previous post about buying multiple trucks, select one for a project the other for a donor. I am building a short wide 66 F100. Recently I purchased a 75 F250 all options(4V-390/c6 ps pb ac) that was a retired/tired farm truck. Kept the things that mattered for the ps, pb, ac, and c6 to bolt to the 4V-352 that is in the 66. Currently have the old ford-o-matic in the truck. Really don't like this tranny. So naturely the c6 is going in. But thought I hit pay dirt when I read about the higher compression ratios on the 4V-390(also kept the short block). I eventually plan to do the 390 in the truck and this ratio(9.5-9.8) is my target. That is an interesting thought about the 410 though. Excuse me for getting a little windy here but ya'll know how it is. Really enjoy this site and visit daily (sometimes multiple times) depending on work load. Later...